Cicero Group head of corporate PR and digital Mike Robb said that the letter should be just the start of the company’s public response to the issue.

‘They must do more than just provide a generic response that everybody expects – they need to back it up with action and outline what they are going to do to change things.’

Yesterday, a number of major brands including Vodafone and BT pulled advertising from the site, which is understood to have 52 million users and about 50 moderators. Prime Minister David Cameron said social network sites had to 'clean up their act' or face boycotts from users.

The Terebin brothers' letter stated they were ‘proud of the phenomenal popularity’ of the social network and pointed to the wider issues around trolling, adding:

‘Bullying is an age-old problem that we in no way condone - and while its evolution online is disturbing, it certainly is not unique to our site.’

The focus on Ask.fm follows Twitter reacting to misogynist tweets aimed at a range of high-profile women including Labour MP Stella Creasy.

Pointing to Twitter’s moves to introduce an in-tweet ‘report abuse’ button on all platforms, Robb said: ‘Ask.fm must be upfront and show what it is doing to address this and not leave a vacuum when it comes to discussing the issue.’

He also highlighted coverage on the wider problem of trolling over recent weeks as having longer-lasting implications for social networking sites.

‘The police can only do so much and there is a big onus now on those who own these sites to take action themselves. Now we’ve seen big name brands withdrawing advertising, it helps set a big precedent for the future. I expect to see a wider reaction in terms of sites looking at how they handle the issue of trolling.’